Length Converter

Length units vary with the job: a drawing may use millimetres, a room measurement may use feet, and a route may use kilometres or miles. Choose the units you have and the units you need, then enter your measurement. The converter includes metric and US customary units, nautical miles, and astronomical units. Each conversion page shows the factor and a worked example.

Length Conversion Guide

Understanding Length Measurements

The SI unit of length is the metre, defined since 1983 as the distance light travels in 1/299,792,458 of a second in vacuum. This definition ties the metre to a physical constant of nature rather than a physical artefact, making it perfectly reproducible anywhere. Derived units (kilometre, centimetre, millimetre, micrometre, nanometre) follow SI decimal prefixes. US customary units (inch, foot, yard, mile) are defined in terms of the metre by international agreement: 1 inch = 25.4 mm exactly.

All conversions in this category are computed relative to a single base unit (Meter) using factors sourced from NIST Special Publication 811 and the BIPM SI Brochure. A shared reference unit keeps the conversion relationships consistent. Converting directly from the original measurement avoids the rounding differences that can accumulate when displayed intermediate results are entered again.

Common Length Units

This calculator supports 11 units, including Meter, Kilometer, Centimeter, Millimeter, Micrometer. Choose the unit shown in your source measurement, then the unit needed for your result.

Units may have alternate spellings or abbreviations. You can search using these names too. Examples include Meter (m, also written as meter or metre), or Kilometer (km, also written as kilometre or kilometers), or Centimeter (cm, also written as centimetre or centimeters).

How to Convert Length Accurately

All length conversions within the SI family are purely multiplicative: you multiply the source value by a fixed conversion factor derived from the ratio of the two unit definitions. Imperial-to-metric conversions use the exact defined equivalences (e.g., 1 inch = 25.4 mm exactly) rather than approximations.

When precision matters, avoid rounding intermediate calculations. The displayed factors and results are rounded for readability, usually to ten significant digits; very large or small values use scientific notation. Use the original measurement for each conversion and round the final answer to match the accuracy of that measurement.

Checking Your Length Conversion

Keep the unit alongside each length value when you copy or share it. Check that the source and target units match your task. If two units have similar names, read their definitions before selecting one.

For a second check, use the worked example and formula on the conversion page. Start from your original value rather than a rounded result from another calculator. If you need to report a specific number of decimal places, round once at the end.

Available Length Units

See full definitions in the unit glossary →

Meter(m)

Also: meter, metre

Kilometer(km)

Also: kilometre, kilometers

Centimeter(cm)

Also: centimetre, centimeters

Millimeter(mm)

Also: millimetre, millimeters

Micrometer(um)

Also: micron, micrometers

Nanometer(nm)

Also: nanometre, nanometers

Mile(mi)

Also: miles

Yard(yd)

Also: yards

Foot(ft)

Also: feet, foot

Inch(in)

Also: inches, "

Nautical Mile(nmi)

Also: nautical miles

Popular Length Converters

Choose a pair below, or browse the full list for other units.

Meter to Kilometerm to km Meter to Centimeterm to cm Meter to Millimeterm to mm Meter to Milem to mi Meter to Yardm to yd Meter to Footm to ft Meter to Inchm to in Meter to Nautical Milem to nmi Kilometer to Meterkm to m Kilometer to Centimeterkm to cm

All Length Converters

Each page has a calculator, a formula, and examples you can check by hand.

Meter to Kilometerm ⇄ km Meter to Centimeterm ⇄ cm Meter to Millimeterm ⇄ mm Meter to Milem ⇄ mi Meter to Yardm ⇄ yd Meter to Footm ⇄ ft Meter to Inchm ⇄ in Meter to Nautical Milem ⇄ nmi Kilometer to Meterkm ⇄ m Kilometer to Centimeterkm ⇄ cm Kilometer to Milekm ⇄ mi Kilometer to Yardkm ⇄ yd Kilometer to Footkm ⇄ ft Kilometer to Inchkm ⇄ in Kilometer to Nautical Milekm ⇄ nmi Centimeter to Metercm ⇄ m Centimeter to Kilometercm ⇄ km Centimeter to Millimetercm ⇄ mm Centimeter to Milecm ⇄ mi Centimeter to Yardcm ⇄ yd Centimeter to Footcm ⇄ ft Centimeter to Inchcm ⇄ in Centimeter to Nautical Milecm ⇄ nmi Millimeter to Metermm ⇄ m Millimeter to Centimetermm ⇄ cm Millimeter to Micrometermm ⇄ um Millimeter to Milemm ⇄ mi Millimeter to Yardmm ⇄ yd Millimeter to Footmm ⇄ ft Millimeter to Inchmm ⇄ in Millimeter to Nautical Milemm ⇄ nmi Micrometer to Millimeterum ⇄ mm Micrometer to Mileum ⇄ mi Micrometer to Yardum ⇄ yd Micrometer to Footum ⇄ ft Micrometer to Inchum ⇄ in Micrometer to Nautical Mileum ⇄ nmi Nanometer to Milenm ⇄ mi Nanometer to Yardnm ⇄ yd Nanometer to Footnm ⇄ ft Nanometer to Inchnm ⇄ in Nanometer to Nautical Milenm ⇄ nmi Mile to Metermi ⇄ m Mile to Kilometermi ⇄ km Mile to Centimetermi ⇄ cm Mile to Millimetermi ⇄ mm Mile to Micrometermi ⇄ um Mile to Nanometermi ⇄ nm Mile to Footmi ⇄ ft Yard to Meteryd ⇄ m Yard to Kilometeryd ⇄ km Yard to Centimeteryd ⇄ cm Yard to Millimeteryd ⇄ mm Yard to Micrometeryd ⇄ um Yard to Nanometeryd ⇄ nm Yard to Footyd ⇄ ft Foot to Meterft ⇄ m Foot to Kilometerft ⇄ km Foot to Centimeterft ⇄ cm Foot to Millimeterft ⇄ mm Foot to Micrometerft ⇄ um Foot to Nanometerft ⇄ nm Foot to Mileft ⇄ mi Foot to Yardft ⇄ yd Foot to Inchft ⇄ in Inch to Meterin ⇄ m Inch to Kilometerin ⇄ km Inch to Centimeterin ⇄ cm Inch to Millimeterin ⇄ mm Inch to Micrometerin ⇄ um Inch to Nanometerin ⇄ nm Inch to Footin ⇄ ft Nautical Mile to Meternmi ⇄ m Nautical Mile to Kilometernmi ⇄ km Nautical Mile to Centimeternmi ⇄ cm Nautical Mile to Millimeternmi ⇄ mm Nautical Mile to Micrometernmi ⇄ um Nautical Mile to Nanometernmi ⇄ nm

Length Converter FAQ

How many length units are supported?

This category supports 11 units: Meter, Kilometer, Centimeter, Millimeter, Micrometer, Nanometer, Mile, Yard, Foot, Inch, Nautical Mile.

How do I convert length units?

Choose a source and target unit, enter a value, and multiply through the m base-unit factors shown on the dedicated converter page.

Which length conversion should I start with?

Choose the pair that matches your measurement. For example, the Meter to Kilometer page shows its formula and worked examples. Related links let you reverse the conversion or choose another unit.

Can I look up length values in a reference table?

Yes. Open a conversion pair to see worked examples and a table of common input values. These reference values remain readable without running the interactive calculator. For an input not listed, use the displayed formula or enter it in the calculator.

How should I round a length conversion?

Match the precision of your original measurement. Keep extra digits during the calculation, then round the final answer to the required decimal places or significant figures. Displaying more digits does not make the original measurement more accurate.